Terpenoids, particularly those with a relatively small molecular weight such as monoterpenes (C10) and sesquiterpenes (C15) serve as major aroma components in plants and are widely used not only as flavors for food products and/or alcoholic beverages, but also even in industrial products including cosmetics and perfumes. It is known that monoterpenes typified by linalool are synthesized within plant cells and are partially accumulated as glycosides. For example, in the case of Arabidopsis thaliana of the family Brassicaceae, a glycoside of hydroxylated linalool has been reported (Non-patent Document 1). Not only in model plants, but also in industrially important crops such as Humulus lupulus of the family Cannabaceae (Non-patent Document 2), Camellia sinensis of the family Theaceae (Non-patent Documents 3 to 6) and Zingiber officinale of the family Zingiberaceae (Non-patent Document 7), monoterpene glycosides are known to be accumulated. Further, because of being widely reported in the plant kingdom (Non-patent Document 8), glycosides would be a common form for precursors of aroma components. From the standpoint of industrial application, studies have also been conducted to artificially control the volatilization of aroma components from terpene glycosides serving as aroma precursors through enzymatic or non-enzymatic cleavage of their sugar moieties (Non-patent Document 9).
However, although β-primeverosidase, an enzyme cleaving the sugar moiety from a monoterpene glycoside, has been previously isolated from Camellia sinensis (Non-patent Document 10), molecular mechanisms for causing sugar addition (i.e., glycosylation) in monoterpenes have not yet been identified. Based on comprehensive activity screening of UDP-sugar dependent glycosyltransferases (UGTs) in Arabidopsis thaliana, some UGT enzymes have been reported to react with monoterpenes in test tubes, but there is no mention of their physiological roles and the significance of their activity (Non-patent Document 11). In Citrus sinensis of the family Rutaceae, monoterpene glycosides are also accumulated, and hence attempts have been made to screen UGTs acting on monoterpenes, but such attempts have not succeeded in identifying any active UGT enzyme gene (Non-patent Document 12).
Humulus lupulus of the family Cannabaceae is a major raw material for beer, and is produced mainly in Europe (e.g., Germany, Czech Republic) and North America (e.g., Canada, USA). Among aroma components responsible for the aroma of beer, those derived from Humulus lupulus include monoterpenes typified by linalool. On the cone surface of Humulus lupulus, there are trichomes called lupulin which are specifically differentiated to accumulate aroma components therein. Many aroma components are considered to be accumulated within lupulin. On the other hand, there are reports showing that glycosides of terpenes (e.g., glycosides of linalool and geraniol) are accumulated as precursors of aroma components in Humulus lupulus and beer, although enzymes for their production have not yet been identified (Non-patent Documents 2, 10 and 13).    Patent Document 1: WO97/11184    Non-patent Document 1: Aharoni et al (2003) Plant Cell 15, 2866-2884    Non-patent Document 2: Kollmannsberger et al (2006) Mschr. Brauwissenschaft 59, 83-89    Non-patent Document 3: Guo et al (1994) Biosci. Biotech. Biochem. 58, 1532-1534    Non-patent Document 4: Nishikitani et al (1996) Biosci. Biotech. Biochem. 60, 929-931    Non-patent Document 5: Moon et al (1996) Biosci. Biotech. Biochem. 60, 1815-1819    Non-patent Document 6: Ma et al (2001) Phytochemisty 56, 819-825    Non-patent Document 7: Sekiwa et al (1999) Biosci. Biotech. Biochem. 63, 384-389    Non-patent Document 8: Winterhalter and Skouroumounis (1997) Adv. Biochem. Eng. Biotechnol. 55, 73-105    Non-patent Document 9: Herrmann (2007) Angew. Chem. Int. Ed. 46, 5836-5863    Non-patent Document 10: Mizutani et al (2002) Plant Physiol. 130, 2164-2176    Non-patent Document 11: Caputi et al (2008) Chem. Eur. J. 14, 6656-6662    Non-patent Document 12: Fan et al (2010) Genome 53, 816-823    Non-patent Document 13: Nedjma, M., et al (2007) Congress Proceedings of European Brewery Convention 71, 1-13